This invention relates to a latching mechanism for a simplified gas fastener-driving tool, in particular, a latching mechanism for use in a combustion chamber of such a tool. Such fastener-driving tools are available commercially from ITW-Paslode (a division of Illinois Tool Works, Inc.) of Vernon Hills, Ill.
Combustion-powered tools, or combustion tools, are known in the art, and one type of such tools, also known as IMPULSE® brand tools for use in driving fasteners into workpieces, is described in commonly assigned patents to Nikolich U.S. Pat. Re. No. 32,452, and U.S. Pat. Nos. 4,522,162; 4,483,473; 4,483,474; 4,403,722, 5,197,646 and 5,263,439, all of which are incorporated by reference herein. Similar combustion-powered nail and staple driving tools are available commercially from ITW-Paslode of Vernon Hills, Ill. under the IMPULSE□□and PASLODE® brands.
Fastener-driving tools are provided with a multitude of components necessary for performing ancillary functions of the tool. One particularly important ancillary function of the tool is scavenging. There are two basic ways that residual combustion products from a combustion chamber are scavenged: a) by dilution, and b) by displacement. The dilution method consists of driving air through the combustion chamber. Usually a fan drives this process. Typically, 2.5 times the combustion chamber volume change is needed to exchange the residual combustion gas with air, making it a relatively inefficient method.
A more efficient process is displacement. The displacement method consists of removing combustion products by reducing the combustion volume to zero, hence displacing the combustion products. Subsequently, when the volume is increased, air is drawn into the volume.
One disadvantage of the current combustion-powered tools used for fastening is that they have a multitude of components that perform the ancillary functions needed to support the basic function of the tool, such as the scavenging function. The use of expensive electronic or electrical components, including batteries, fan motors, control electronics and spark electronics for these ancillary functions is known.
A further disadvantage of these tools having complex components is that the additional components make the tool more susceptible to costly repairs.
Another approach to scavenging is taught by U.S. Pat. No. 4,712,379 to Adams, incorporated by reference herein, which discloses a combustion chamber divided by a movable plate with holes. The use of this approach accelerates the rate of combustion so that the combustion pressure reaches a maximum early in the drive stroke of the free piston. The acceleration in the rate of combustion is due to the turbulence created in the combustion chamber when the fuel-air mixture passes through the holes in the movable plate.
An advantage of using the movable plates is that the piston is shielded from the pressure increase in the first chamber where the combustion is initiated. A further advantage is that the combustion in the first chamber creates a flame that passes through the holes in the movable plate, and ignites the second chamber earlier in the piston's cycle. The earlier the pressure reaches its maximum in the piston drive stroke, the more energy is delivered to the fastener being driven, and ultimately, the work piece.
Another ancillary function of fastener-driving tools is to establish the correct fuel-air mixture needed for efficient combustion. This process is more difficult in the divided combustion chamber approach. Known solutions to establishing the correct fuel-air mixture include independently introducing the correct amount of fuel to each chamber or premixing the fuel and air in a pre-chamber before they are drawn into the divided combustion chamber.
One disadvantage is that these approaches involve additional components to support the mixing process. A further disadvantage is that these known approaches often cannot accommodate the tool when a rapid cycle is desired.
Thus, there is a need for a fastener-driving combustion tool with movable plates that does not require electric or electronic parts. There is also a need to provide a fastening tool combustion chamber that achieves the correct fuel-air mixture. Another need is to provide a fastening tool combustion chamber where the piston is shielded from the pressure increase in the first chamber where the combustion is initiated. There is also a need to provide the turbulance to achieve rapid burn. A still further need is to provide a fastening tool combustion chamber where the pressure is delivered to the piston early in its drive stroke. Yet another need is to provide a fastening tool combustion chamber that is less expensive to manufacture. Still another need is to provide a fastening tool combustion chamber that is less susceptible to costly repair. A further need is to provide a fastening tool combustion chamber that precisely controls the movement of the plates in the combustion chamber.